relocate dbmeta models to discordid

While we're about to introduce more metadata structs, it seems like
mautrix-slack keeps these in slackid, so let's keep ours in discordid.

pkg/discordid/dbmeta.go

@@ -0,0 +1,24 @@
+// mautrix-discord - A Matrix-Discord puppeting bridge.
+// Copyright (C) 2026 Tulir Asokan
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+package discordid
+
+import "github.com/bwmarrin/discordgo"
+
+type UserLoginMetadata struct {
+	Token            string                     `json:"token"`
+	HeartbeatSession discordgo.HeartbeatSession `json:"heartbeat_session"`
+}